Respiratory failure in severe trauma

Can blood gas results be used to predict respiratory failure in victims of severe trauma? Many such patients present with metabolic acidosis, invariably the result of increased lactic acid production due to hemorrhagic shock. The normal physiological (compensatory) response to preserve a normal pH in those with metabolic acidosis is increased respiration to reduce partial pressure of CO2. 

A normal pCO2 is thus inappropriate in metabolic acidosis. Clinicians at the University of Hawaii School of Medicine designed a study to test the hypothesis that failure of trauma patients with metabolic acidosis to reduce pCO2 by hyperventilating and thereby compensate for their acidosis indicates impending respiratory failure and the need for intubation. 

They retrospectively reviewed the medical records of all 2601 trauma patients admitted to their department over a two-year period. From this database they identified 140 patients whose blood gas results on admission indicated they were suffering metabolic acidosis. 

Some of these patients were found to have an appropriately reduced pCO2 (the compensated group) and the remainder had either a normal or inadequately reduced pCO2 (the uncompensated group). Of the 140 study patients, 45 subsequently required intubation and ventilatory support; the remaining 95 did not require intubation. 

Statistical analysis revealed that the ability to mount a compensatory respiratory response to metabolic acidosis was an independent predictor of intubation. Those whose metabolic acidosis on admission was uncompensated were 4.2 times more likely to require subsequent intubation compared with those whose metabolic acidosis was appropriately compensated.